SIU 2018: Advances in Renal Imaging for Tumor Tissue Characterization

Seoul, South-Korea (UroToday.com) Dr. Gaitonde provided a brief update to advances in renal imaging for tumor tissue characterization.  Renal masses are often incidentally found nowadays, often on non-contrast imaging done for other reasons. As such, we are seeing a lot of patients with renal masses – many of whom may not require treatment. ~25-30% of masses < 4 cm are benign – but at this time, we don’t have reliable imaging modalities to identify patients who can avoid treatment.
 
Suffice it to say that the technology has drastically improved and, despite recent studies demonstrating its efficacy, current guidelines do not advocate for routine renal tumor biopsies. It is only recommended when non-RCC histology is suspected or patient is not a surgical candidate – basically when looking for a reason to not offer intervention.

Currently, CT imaging (axial cross-sectional imaging with contrast) is the standard of care evaluation for renal masses. We know that masses without contrast enhancement are likely to be benign. Evaluation requires 4 phases: non-contrast, corticomedullary phases, nephrogenic phase and delayed phase. Using this, we can pretty accurately assess renal masses – but it does not tell us about benign tumors or about the histology of malignant tumors. 
  • It does have high sensitivity and specificity for RCC
  • Inaccurate for the identification of oncocytoma
There are multiple new modalities that may be able to help improve on the current standard.

1. mpMRI – as with prostate evaluation, this requires multiple phases (T1, T2, Diffusion Weight Imaging, Dynamic contrast enhancement)
  • It has high sensitivity and specificity for renal masses (88-100% sensitivity, 83-93% specific)
  • “Solid Renal masses: What the Numbers Tell Us” 1 – MRI is already the most effective tool available!
  • MRI outperforms CT when differentiating oncocytoma from RCC – however, its still not perfect
  • However, major limitation has been urologist inability and discomfort with interpreting these images – but if we order more regularly, it may actually be a better tool!
2. Contrast-enhanced ultrasound
  • There has been increasing use of contrast-enhanced ultrasound (CEUS) outside the United States – which has the benefit of being simple, short, and without radiation risk.
  • It has some benefits over CT
  • It is better at evaluating hypovascular areas through background suppression
  • It also is able to better evaluate the enhancement of septations in complex cysts
  • Better than CT at differentiating cyst from solid mass
  • CEUS has been validated as a measure of Bosniak classification
  • It has high sensitivity and specificity for malignant tumors (100% and 95%, respectively) – PPV 95% and NPV 100%
  • This is a tool that warrants more research and attention!
3. CT Texture analysis
  • This is a new technology with limited data
  • It specifically assesses vascular heterogeneity
  • Most of the work in this technology has been focused on liver and lung pathology
  • Preliminary pilot study demonstrates high sensitivity and specificity for malignant RCC, ccRCC and oncocytoma. Sens/specificity exceeded 90% for all of these2
This is a promising new technology that may augment current CT technology

4. Nuclear Medicine imaging
  • Currently, the Technetium-99 Sestamibi scan (traditionally used by cardiologists and endocrine surgeons) may have a role in differentiating oncocytoma3, 4
  • Two studies that assessed the efficacy in this space
  • Not perfect, but distinguishes oncocytoma from RCC pretty well - 80-90% accurate for oncocytoma
Obviously there is a huge need for improved non-radiating imaging in the evaluation and monitoring of renal masses. This is a work in progress, with promise in the areas of CEUS and mpMRI. 

Presented by: Krishnanath Gaitonde, University of Cincinnati, Cincinnati, Ohio, United States

References: 
1. Kang et al. AJR 2014.
2. Raman et al. Acad Rad. 2018
3. Gorin et al. 2015.
4. Tzortakakis et al. 2017. 

Written By: Thenappan Chandrasekar, MD, Clinical Instructor, Thomas Jefferson University Twitter: @tchandra_uromd, @TjuUrology at the 38th Congress of the Society of International Urology - October 4- 7, 2018 - Seoul, South Korea
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